My first build, help and ton of questions!!!

Hey everybody, this is my first time here and this is my first time to build a audio construction thingy... Im about to buy a new Mitsubishi lancer GTS 2009 (about 2 months from now on) so... I plan to working on this construction try to figure it out the prices, tons of internet shop and please help me with these question on the map, correct me and give me some advise lovely people.... thz for thousand time...